So I have figured out what was my problem with building Firefox... as Ted Mielczarek pointed out I was changing the .mozconfig.mk file within the Mozilla directory thinking thats the configuration file when in fact it is actually .mozconfig without the .mk extension as .mozconfig.mk is auto generated by the build script (which would also explain why it was overwriting the file each time I ran the build command).
In any case I fixed that and then ran the build command once again. It started the build and after 9 very long hours (yes 9 hours) it told me that there were errors so it aborted the compilation. So what I did was create a new folder on my C drive then I re-downloaded the client.mk file and then checked out the code once again. I then created a .mozconfig file and placed it in the Mozilla directory and ran the build command. 10 long hours later the build was complete and I had a running version of Minefield.
I'm now in the process of building on Fedora 7 which I installed on a virtual machine on my desktop. Hope it goes smoothly and will post an update when its done.
The build on Fedora went fine... in fact I would say better than fine since it only took a little over 70 minutes. But what is strange about this is that both builds were done on the same hardware... the first being in Windows XP SP2 with 1GB of RAM and the second in Fedora 7 running inside XP on a virtual machine, with a mere 256MB of RAM -- a quarter of the memory that was available during the first build. Whats even stranger is that this was a debug enabled build where as the one on XP was not. Someone on IRC (andrew) was suggesting that this may be due to my anti virus software so if you haven't compiled Firefox yet you may want to consider shutting down your AV for the duration of the build when you get around to it.